Method of manufacturing porous metallic bodies



' 1; .lie powders.

Patented June 1, 1937 METHOD. OF MANUFAc'runmG ronous METALLIC nonmsnuaou Schulz,"Stuttgart, Germany a I no Drawing. Application June 14,1934, Serial No. 730,677. In Germany June 15, 1933 12 Claims. (CI.75-22) This methodrefers' to manufacturing porous metallic bodies ofevery kind. There are already known numerous proceedings ofmanufacturing rcus metallic bodies all of which were found- 5 ed on theidea to obtain, with relatively low temperatures, a'sintering as rapidand easy as possible, in order to maintain in the thus composedmaterials a greatest possible porosity; it has been ascertained,however, that such materials, made according to the proceedings known upto this day-suffer important shrinking and consequently condensationunder prolonged heat treatment. The opinion-existed that a great volumeof pores wasonly obtainable with easily sintering metal- A proceedinghas for instance become known, in which the initial .product is ametallic powder obtained by the sintering together of metals obtainedfrom carbonyls, because just such tiny particles sinter together par-'ticularlyveasily and quickly in consequence of their condition of.surface. Contrary to the above mentioned proceedings any metallic powderis chosen according to the present methodi however, its composition;mustbe, either through different 'conditions or through previoustreatment of different duration of the separate, under certaincircumstances completely homogeneous ingredients, that the ingredient,forming, as it were,a rigid frame or skeleton, shows, during the heatprocess, which causes the sintering, no, or at the utmost insignificant,appearances of shrinking. Y

According to the present invention the small method.

skeleton particles are obtained by the following As initial materialthere is generally a highly active, exceedingly fine metallic powder,susceptible to sintering, which may be obtained byprecipitation or byreduction from oxide powder.

. 40 This metallic powder is exposed to a suitably long heat-treatmennin absence of oxygen or in presence of reducing gases, as for instancehydrogen.

The temperature and the duration of the first sintering are chosen suchas to form a coherent but easily crumbling mass cake. This mass cakesubjected in further successive steps in the same' manner to ananalogous heat treatment, whereby the separate little grains always baketogether and form anew a friable mass cake. With these separateprocesses of heat treatment the single 5 small grains condense more andmore intheir' inner structure; In each mechanical trituration takingplace after each sintering the mass cakes sinteredtogether. crumbleessentially again into the small particles obtained after the first.sin- 10 by the following example of copper obtained from' oxide. Black,finely divided copper oxide arranged in. a loose mass is reduced in ahydrogen atmosphere at a comparatively low temperature. In order tomaintain this low temperature, it is necessary when large amounts ofcopper oxide areused, to add an inert gas, for instance, nitrogen, tothe hydrogen atmosphere, in an amount up to The mass obtained after thereduction is ground and is then passed through a sieve. The uniformgranulated material thus obtained may be. de-

scribed as an active material, since it sinters and since its volume isreduced during the sintering process.

In order to obtain the other component whichis necessary for theproduction of porous bodies in accordance with the present invention, itis possible either to subject these active particles to a furthertreatment or to use a different material 35 which is obtained in exactlythe same way as the active granulated substance by a reduction of copperoxide,- and which is passed through a sieve. The following procedure maybe used:-

Copper granules which have been reduced at a comparatively lowtemperature and then comminuted and passed through a sieve, are arrangedin a loose heap and are heated for four hours in a hydrogen atmosphere.A black, adhe'rent mass is formed which is then very care- 45 fully.comminuted, not so much by grinding as by' As used throughout thisspecification, the term non-shrinkable particles or skeleton particlesis used to describe a substance, the density of which can be increasedonly with great difiiculty by a diminutionpf its volume; this term hasno reference to the expansion and contraction of a substance caused byvariations in temperature.

An essential point of this proceeding is further, the possibility ofsoldering together, respectively of sintering together massive metallicobjects with the porous metallic body. To this purpose essentiallylonger heat treatments and such of generally higher temperatures arenecessary, than those employed for instance in the manufacture ofmetallic bodies of carbonyl: metal-powder. The shrinking which alwaystakes place with a similar treatment, hitherto was an unsurmountableobstacle for the manufacture of porous compound-metal-bodies bysintering. By mixing the ingredients which form the no more shrinkingscaffold with finer ingredients which eventually are subject also to agreater shrinking, it is possible, to choose and to determine beforehandthe porosity and size of pores within certain limits in a quitedetermined way.

If porous metallic bodies, obtained at a com paratively low temperatureand in a comparatively short time from specially quick-sinteringmetallic powder, are subjected in the practice to a heat treatment oflonger duration, as a rule a considerable shrinking takes place, wherebyat the same time, the size of the pores decreases, and destroying cracksappear on generally the Whole porous body.

'To the contrary, if a change takes place at all, the change of porosityof the bodies made according to this new method, moves just in thecontrary sense, viz. in thedirection of greater porosity, the outervolume remaining unchanged.

On account of the stability of volume of the metallic bodies preparedaccording to this proceeding, any granulous or powdered ingredients maybe added to the initial powder or mixture of powder, for instanceoxides, mineral sub.- stances or the like without any detrimentalinfluence to the' good mechanical qualities of the originatedporousmetallic bodies.

I claim:

1. The method of manufacturing porous metallic bodies,.which comprisesmixing a metallic powder consisting of particles of a comparativelylarge size with a powder consisting of particles of the same metal of acomparatively small size, the first-mentioned particles beingsubstantially less compressible than the second-mentioned particles andsintering the mixture in the absence of oxygen and pressure at atemperature which is lower than the melting point of said metal.

2. The method of manufacturing porous metallic 'bodies, which comprisesmixing a powderv consisting of particles of a metallic alloy of acomparatively large size with a powder consisting of particles of thesame metallic alloy of a comparatively small size, the first-mentionedparticles being substantially less compressible than the secondmentioned particles and sintering the mixture in the absence'of oxygenand pressure at a temperature which is lower than the melting point ofsaid metallic alloy.

3. The method of manufacturing porous metallic bodies, which comprisesmixing a powder consisting of particles of a metallic alloy of acomparatively large size with a powder consisting of particles of a:metal of a comparatively 'small size, the first-mentioned particlesbeing compressible than the first-mentioned particles,

and sintering this mixture in the absence of oxygen and pressure at atemperature which is lower than the melting points of said metallicpowders.

5. The method of manufacturing porous metallic bodies, which comprisesreducing a metal compound in a reducing atmosphere at a low temperatureobtained by diluting the reducing gas by an inert gas to produce ametallic powder consisting of particles of a comparatively small size,mixing said metallic powder with a metallic tively large size which aresubstantially less compressible than the first-mentioned particles, and

sintering this mixture in the absence of oxygen and pressure at atemperature which is lower than the melting points of said metallicpowders.

6. The method of manufacturing porous metallic bodies, whichcomprises'reducing a mixture of metallic compounds, each of whichcomprises at least one of the components of a metallic alloy,

powder consisting of particles of a comparain a reducing atmosphere at alow temperature to produce a powder consisting ofparticles of a metallicalloy of a comparatively small size, mixing said powder with a powderconsisting of metallic particles of a comparatively large size which aresubstantially less compressible thanthe first-mentioned particles, andsintering this mixture in the absence of oxygen and pressure at atemperature which is lower than the melting points of said powders.

7. The method of manufacturing porous metallic bodies, which comprisessintering a finely divided loose metallic powder in a reducingatmosphere at a temperature which is considerably lower than the meltingpoint of said metallic powder, whereby said powder forms a cake,comminuting said cake to provide a metallic powder having particles of acomparatively large predetermined size, subjecting the powder thusobtained a number of times to a sintering procws resulting in theformation of a cake and a subsequent oomminuting of this cake until ametallic powder is produced, which consists of particles of acomparatively large size, mixing the lastmentioned powder with a powderconsisting of metallic particles of a comparativelysmall size, thefirst-mentioned particles being substantially lesscompressible than thesecond-mentioned particles and sintering the mixture in the absence ofoxygen and pressure at a temperature which .is lower than the meltingpoints of the powder, whereby said powder forms a cake, com- 1| minutingsaid cake to provide a metallic powder 4 and then reducing the surfacesof some or the body. so

last-mentioned particles, whereby particles oi a comparatively smallsize are produced which are mixed with the particles of a comparativelylarge size, and sintering the resultantvmixture in a reducing atmosphereat a temperature which is lower than the particles.

9. The method 'of manufacturing porous me tallic bodies, whichcomprisesmixing a metallic powder consisting of particles of a comparativelylarge size with a powder consisting of metallic particles of acomparatively small size the ilrstmentioned particles beingsubstantially less compressible than the second-mentioned particles,immersing a metallic body into said mixture, and sintering the mixturealong with the metallic body in the absence of oxygen and pressure at atemperature which is lower than the melting points at said metallicpowders and said metallic 10. The method tallic bodies, which comprisesmixing a metallic powder consisting of particlesoi. a comparativelylarge size with a powder consisting of metallic particles of acomparatively small size, the firstmentioned particles beingsubstantially less com pressible than the second-mentioned particles,mechanically 'roughening some oi the surfaces of a metallic body,immersing said metallic body-into said mixture, said mixturebeing incontact with theroughened surfaces or said body. and sintermeltingpoints of the metallic of manufacturing porous me-f points ing themixture along with the metallic body in the absence or oxygen andpressure at a temperature which is lower than the melting points of saidmetallic powders and said metallic body.

ll..The method of'manufacturing porousrnetallic bodies, which comprisesmixing a metallic powder consisting of particles of a comparativelylarge size with a powder consisting of metallic particles of acomparatively small size, the firstmentioned particles beingsubstantially less'compressible than the second-mentioned particles;subjecting some of the surfaces of a metallic body to an oxydation and asubsequent reduction,

whereby said surfaces are roughened, immersing said metallic body intosaid mixture, said mixture being in contact with the roughened surfacesof said body, and sintering the mixture along with the metallic body in.the absence of oxygen and pressure at a temperature which is lower thanthe melting points of said metallic powders and said metallic body.

12. The method of manuiacturing porous metallic bodies, which comprisesmixing a metallic powder consisting of particles of a comparativelylarge size with a powder consisting of metallic particles of acomparatively small size, the thatmentioned particles beingsubstantially less comm'e'sslble than the second-mentioned particles.subjecting-some of the surfaces oi a metallic body to an oxydation toroughen the same, im-

' mersing said metallic body into said mixture, said mosphere and in theabsence of pressure at a temperature which is lower than the meltingRUD'.

of said metallic powders and said metallic

